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U.S. Climate Normals
Beginning August 1, 2011, the U.S. ASOS maps and the monthly mean maximum and minimum temperature anomaly maps will be using the newly updated 1981-2010 Normals to calculate anomalies. Other 30-year Normals anomaly-based monitoring products will not be affected by the Normals transition until early 2012.
Climate Normals are three-decade averages of climatological variables. The most widely-used Normals are those for daily and monthly station-based temperature, precipitation, snowfall and heating and cooling degree days. These come from NOAA's Cooperative and First-Order station networks. Meteorologists and climatologists regularly use Normals for placing recent climate conditions into historical context; such as comparisons with the day's weather conditions on local television. Normals are also utilized in many applications across a variety of sectors. These include regulation of power companies, energy load forecasting, crop selection and planting times, construction planning, building design, and many others.
Several changes and additions will be incorporated into the 1981-2010 Normals. Monthly temperature and precipitation Normals will utilize underlying data values that have undergone additional quality control to account for things such as stations having been moved. Unlike the 1971-2000 Normals, daily (rather than monthly) data will be used extensively in daily temperature Normals as well as heating and cooling degree day Normals, providing greater precision of intra-seasonal features. More details can be found in Arguez et al. 2011.
When the new Normals are released, relevant comparisons between the new version and previous versions will be highlighted. Observational evidence shows that the 2000-2009 timeframe was the warmest decade on record in the U.S. Therefore, we expect that the new Normals will generally be warmer on average for most stations, but not uniformly warmer for all stations and all seasons. In fact, some station Normals in certain seasons will become cooler.
Information on the current Normals, as well as the history of the Normals, can be found on NCDC's U.S. Climate Normals webpage. For general questions about Normals or help accessing the 1971-2000 product, please contact NCDC's Customer Services Branch.